Re: [PATCH v3 net-next 5/6] tcp: add tcp_comp_sack_delay_ns sysctl

[Neal Cardwell]

On Thu, May 17, 2018 at 5:47 PM Eric Dumazet  wrote:

> This per netns sysctl allows for TCP SACK compression fine-tuning.

> Its default value is 1,000,000, or 1 ms to meet TSO autosizing period.

> Signed-off-by: Eric Dumazet 
> ---

Acked-by: Neal Cardwell 

Thanks!

neal

[PATCH v3 net-next 5/6] tcp: add tcp_comp_sack_delay_ns sysctl

[Eric Dumazet]

This per netns sysctl allows for TCP SACK compression fine-tuning.

Its default value is 1,000,000, or 1 ms to meet TSO autosizing period.

Signed-off-by: Eric Dumazet 
---
 Documentation/networking/ip-sysctl.txt | 7 +++
 include/net/netns/ipv4.h   | 1 +
 net/ipv4/sysctl_net_ipv4.c | 7 +++
 net/ipv4/tcp_input.c   | 4 ++--
 net/ipv4/tcp_ipv4.c| 1 +
 5 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.txt 
b/Documentation/networking/ip-sysctl.txt
index 
ea304a23c8d72c92a925d0c107bfd2bcfbbb92ec..7ba952959bca0eee4ecf81fb5837e17790db0fde
 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -525,6 +525,13 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max
 tcp_sack - BOOLEAN
Enable select acknowledgments (SACKS).
 
+tcp_comp_sack_delay_ns - LONG INTEGER
+   TCP tries to reduce number of SACK sent, using a timer
+   based on 5% of SRTT, capped by this sysctl, in nano seconds.
+   The default is 1ms, based on TSO autosizing period.
+
+   Default : 1,000,000 ns (1 ms)
+
 tcp_slow_start_after_idle - BOOLEAN
If set, provide RFC2861 behavior and time out the congestion
window after an idle period.  An idle period is defined at
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 
8491bc9c86b1553ab603e4363e8e38ca7ff547e0..927318243cfaa2ddd8eb423c6ba6e66253f771d3
 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -160,6 +160,7 @@ struct netns_ipv4 {
int sysctl_tcp_pacing_ca_ratio;
int sysctl_tcp_wmem[3];
int sysctl_tcp_rmem[3];
+   unsigned long sysctl_tcp_comp_sack_delay_ns;
struct inet_timewait_death_row tcp_death_row;
int sysctl_max_syn_backlog;
int sysctl_tcp_fastopen;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 
4b195bac8ac0eefe0a224528ad854338c4f8e6e3..11fbfdc1566eca95f91360522178295318277588
 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -1151,6 +1151,13 @@ static struct ctl_table ipv4_net_table[] = {
.proc_handler   = proc_dointvec_minmax,
.extra1 = ,
},
+   {
+   .procname   = "tcp_comp_sack_delay_ns",
+   .data   = _net.ipv4.sysctl_tcp_comp_sack_delay_ns,
+   .maxlen = sizeof(unsigned long),
+   .mode   = 0644,
+   .proc_handler   = proc_doulongvec_minmax,
+   },
{
.procname   = "udp_rmem_min",
.data   = _net.ipv4.sysctl_udp_rmem_min,
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 
cc2ac5346b92b968593f919192d543384865bcb8..6a1dae38c9558c7bc9dd31e9f16c4e8ea8c78149
 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5113,13 +5113,13 @@ static void __tcp_ack_snd_check(struct sock *sk, int 
ofo_possible)
if (hrtimer_is_queued(>compressed_ack_timer))
return;
 
-   /* compress ack timer : 5 % of rtt, but no more than 1 ms */
+   /* compress ack timer : 5 % of rtt, but no more than 
tcp_comp_sack_delay_ns */
 
rtt = tp->rcv_rtt_est.rtt_us;
if (tp->srtt_us && tp->srtt_us < rtt)
rtt = tp->srtt_us;
 
-   delay = min_t(unsigned long, NSEC_PER_MSEC,
+   delay = min_t(unsigned long, 
sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
  rtt * (NSEC_PER_USEC >> 3)/20);
sock_hold(sk);
hrtimer_start(>compressed_ack_timer, ns_to_ktime(delay),
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 
caf23de88f8a369c2038cecd34ce42c522487e90..a3f4647341db2eb5a63c3e9f1e8b93099aedadab
 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2572,6 +2572,7 @@ static int __net_init tcp_sk_init(struct net *net)
   init_net.ipv4.sysctl_tcp_wmem,
   sizeof(init_net.ipv4.sysctl_tcp_wmem));
}
+   net->ipv4.sysctl_tcp_comp_sack_delay_ns = NSEC_PER_MSEC;
net->ipv4.sysctl_tcp_fastopen = TFO_CLIENT_ENABLE;
spin_lock_init(>ipv4.tcp_fastopen_ctx_lock);
net->ipv4.sysctl_tcp_fastopen_blackhole_timeout = 60 * 60;
-- 
2.17.0.441.gb46fe60e1d-goog